Newton’s Laws

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Vectors and scalars

VectorsA quantity that has 2 dimensions,

MAGNITUDE and DIRECTIONScalars

A quantity that has a single dimension MAGNITUDE

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Vectors and scalars

Term Definition Vector or Scalar

displacement

temperature

Speed

Velocity

Distance

Acceleration

Forces

Weight

deceleration

mass

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Forces F=MA

Forces cause ; A force is a

“A force is that which alters or to alter a body’s or of in a line.”

If a body changes or , a has been applied

force

movementpush or a pull

tendsstate of rest

uniform motion straight

direction velocity

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Forces affecting motion

External Reaction forces Gravity Air resistance/friction

Internal Muscular

contractions

Vertical Weight – mass x

acceleration Gravity Air resistance/friction Reaction force

Horizontal Friction Air resistance

Impulse

Impulse = force x time

The length of time a force is applied to an object or body and therefore change in momentum

Sporting examples?

Reaction force

Reaction force always occur when 2 bodies are in contact

Act at 90 degrees to contacted surface

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Forces affecting motion

Unbalanced Where a force acting in 1

direction is larger than that acting in the opposite direction

Object or body will start to move or accelerate/decelerate in the direction of the bigger force

Balanced 2 or more forces are

of equal size but in opposite direction

All the forces cancel themselves out so zero net force

Object or body will remain stationary or remain constant in its velocity

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Ground Reaction Force

Action force of muscle contraction

Equal and opposite Ground Reaction Force

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Forces applied - runner

‘action force’ applied to ground Reaction force from between ground and foot Air resistance

Muscular

groundGravity

Friction

to forward motion

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Forces acting on a sprinter

Action force of muscular contraction

Friction

Gravity

Air resistance

Equal and opposite Ground Reaction Force

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Forces applied – high jumper

‘action force’ applied to ground

Reaction force from - large vertical component

between ground and footAir resistance

Muscular

ground

Gravity

Friction

to forward motion

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Forces applied – kicking

forces applied to ballReaction force from

between ball and footAir resistance

Muscular

ballGravity

Friction

to forward motion

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Newton’s Laws

• 1st Law –

• A body will remain in its / until affected by a

• A body has a to change its

Law of inertia

state of motion

reluctance

rest force

state of motion

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Applying Newton’s 1st Law

• Sprinter remains in on blocks until a causes him to change his

• Ball keeps moving until a causes it to change its

force

set positionforce

state of motion

state of motion

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Momentum

In sporting situations, remains constant; therefore inertia

All objects in motion have mass and

Product = Momentum = mass x velocity

mass

stays the same

velocity

momentum

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Newton’s Laws

• 2nd Law –

• The rate of change of is to the force causing the change, and the change takes place in the in which the force was applied • In sport, remains constant and therefore momentum equates to

Law of acceleration

momentumdirectly proportional

directionmass

acceleration

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Applying Newton’s 2nd Law

• The (size) and of force applied by the sprinter to the blocks determines the and of received – because mass remains constant• Acceleration is to applied•

magnitude direction

magnitude directionacceleration

proportional force

F = ma

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Newton’s Laws

• 3rd Law – Law of Reaction

• To every force there is an and reaction force

equal

opposite

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Applying Newton’s 3rd Law

The sprinter applies a to the ground. This results in a force causing movement

The sprinter cannot move the

Reaction force from ground =

muscular forcereaction

earth/blocks

Ground Reaction Force

Extended work

Tomorrow’s lesson, you will be in groups of 4.

With use of video camera and practical performer you will apply Newton’s 3 Laws of Motion to your choice of a sporting situation

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Typical question

Use Newton’s Three Laws of Motion to explain how a tennis player moves towards the ball in preparation to play a stroke. (5 marks)

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Answer

First Law – reluctance to change state of motion/constant motion/ uniform motion/velocity;Force required to change state of motion/overcome inertia of player;Muscle contractions; (Sub max 2 marks)

Second Law – magnitude/size of force governs change in momentum;Mass remains constant;Force governs magnitude of acceleration given to player;And direction; (Sub max 2 marks)

Third Law – equal and opposite reaction force;Force applied to ground/ moves performer;Ground Reaction Force. (Sub max 2 marks)

Max of 5 marksDo not credit Force = Mass x AccelerationOnly credit responses that relate to the player not the ball.